1. Field of the Invention
The present invention relates to digital computers, and more particularly to an aerospace computer for missile control having a microprogrammed processor.
2. Description of the Prior Art.
The concept of microprogramming was first introduced by M. V. Wilkes, "The Best Way to Design an Automatic Calculating Machine", Report of Manchester University Computer Inaugural Conference (July 1951), as a systematic way of designing the control section of a digital computer. His approach consists of providing the control section with an autonomous read only storage. Each time a program instruction begins, the control unit generates an address to its read only storage derived from the operation code (opcode) of the instruction. This location provides the first of a series of words which supply the control signals to the computer for carrying out the particular instruction being processed. Each instruction in effect generates a transfer to a microsubroutine associated with it, and the resultant step by step operation of the machine corresponds to the execution of a program on a very detailed level (thus the term microprogram).
These proposals were not widely implemented at the time of Wilkes'initial work in the early 1950's due to hardware limitations. However, the present availability of integrated circuit read only memories has made the construction of a microprogrammed computer feasible.
Additionally, a computer memory provides the largest hardware cost in a computer. Therefore, the key to hardware speed and minimum size lies in efficient use of the memory. Fixed instruction length computers require the same number of bits per each instruction word regardless of the simplicity or complexity of the operation to be executed. As an example, many bits can be wasted in instructions which specify simple operations, while many instructions can be wasted in complex operations where an instruction's capability is limited by its length.
Also, computers are designed according to one of three architectures: accumulative, list processor or general register. Except for special applications, the general register computer yields the most efficient use of memory. For most efficient operation it is desired to design a computer which can perform all applications most efficiently.